Two subwoofers for two channel music listening

pre-sub-amp-mains

To make it easier for your amp, and for your mains: go preamp line out to self-powered sub.

then sub sends everything but low bass to the amp

then amp to mains.

amp does not have to amplify low bass signals (they are the biggest power need).

mains do not try to make low bass, also the hardest to do. this lets them do an easier and cleaner job of highs, mids, upper bass.

this allows a less powerful amp to be used, and that especially makes it easier to try tubes.

smaller amp = less: money; size; weight; heat. = more placement options.

Bass is STEREO, place front firing subs adjacent to mains, to achieve bass imaging.

It is not just the bass fundamentals, also the overtones that give localization.

The bulk of what you get (except organs/1812) will not be super low bass, A great deal of what you listen to will have low bass, discernable locations. Presumably you mains do not handle low bass as well as you would like.

I have two very powerful 15" in my speakers, you could think of them as subs. They definitely produce stereo bass.

I listen to a lot of Jazz trios, quartets, even bigger groups, with nice imaging of bass players.

IF piano is off center, and IF recorded/mixed properly, low notes are definitely discernable by location.

Yes, organ is Mono, but many other instruments locations are discernable

not complete, but a quickie find showing which (not that many) instruments get way down there into the 'mono bass' range

https://www.researchgate.net/figure/Frequency-ranges-of-several-musical-instruments-30_fig3_22844644...

More than 2 SUBS, SWARMS. Sacrifice Directionality for Extension?

People who want very/extremely lows produced cleanly will use more than 2 subs, sometimes multiple ’Swarms’ which has been discussed here. I’ve never heard that except a swarm of bees chasing me, and that is directional, i.e. run this way.

Swarms, more than 2 subs get super lows, however the results are MONO BASS, even the upper bass will be mono because the fundamentals and overtones emanate from too many locations, and reflect off too many surfaces..

Some use ported mains and/or ported subs. I recommend only front firing ports, again to retain directionality.

I much prefer decently low bass with imaging than a bit more bass.

In my exuberant youth, I, with help from Electro-Voice Engineering department, designed these enclosures with optional ports, to squeak more bass from these 15", which I measurably got.

However, they are rear facing ports. Less pressure in the enclosure, the front 15's go lower. Additional output from the tuned port and rear surface of the woofer, that gets to rear wall/corners. Even more extension, but they muddy the directionality of both the extended bas, also all it's output, fundamentals and overtones muddy everything else.

It's a trade off. I keep the ports closed. Why sacrifice directionality of a lot of low content for most of my music to get more bass infrequently or rarely?.

Remote Control of Sub(s) sounds terrific, initial setup from a few listening spots. After that, remote volume would be very nice.

A crossover has to exist somewhere, to separate low bass from everything else. Home theater receivers have built in, and the content coding has separate bass.

2 channel amps for music systems typically do not have crossovers built in. You can use a self powered sub’s built in crossover, that is the method that makes it easier for the amp and mains because they do not have to produce low bass.

A separate external crossover does the same thing, except you have more control of the quality of that device. And you do not need to get any signal back from the sub. Crossover sends lows to sub, everything else (easier job) to the amp(s) which send signals with no low bass (easier job) to the mains. 

http://www.acousticfrontiers.com/three-ways-to-add-a-subwoofer-crossover-to-your-two-channel-system/

Many subs have crossovers built in, some line in, some speaker wires in, some both. If via speaker wires, the amp is still producing low bass, then the sub filters that for itself, and sends speaker wires to your mains. This gives the mains a break, but does not give the amp a break.